Abstract Improving the family environment, service access, and behavioral adjustment of children with Autism Spectrum Disorder (ASD) has high relevance both for the children and their families as well as for health care and service payors. Family environment is a critical influence on ASD children?s adjustment: Poor parent adjustment increases behavior problems in ASD children, reduces parents? capacity to access and adhere to critical services, and dampens or eliminates the benefits of early intervention. However, due to the stressors of navigating ASD-related and medical services, as well as managing child behavior challenges, parents of children with ASD report low levels of individual and couple adjustment. Parents report high levels of depression and anxiety, and low levels of parental efficacy and couple relationship quality compared to parents of typically developing children. To address the dual needs of parents for support in navigating ASD services and maintaining positive family functioning, we propose to test Autism Parent Navigators (APN), an innovative in-home, peer support model for parents with a young child recently diagnosed with ASD. APN was designed to be feasible and scalable by relying on parent peer mentors to conduct sessions. Extensive pilot work over the past 3 years has generated evidence of feasibility, acceptability, and impact. This pilot work has allowed us to fine-tune the parent mentor training, participant recruitment, delivery, and fidelity monitoring procedures. Aim 1. To assess the efficacy of APN in a randomized trial with 180 families. Aim 2. To test the mediating pathways through which APN impacts outcomes: We will test whether impact on proximal targets (ASD-related appraisals; coparenting; parent self-efficacy about accessing services; and peer mentor support) influence parent mental health, parenting, and treatment engagement, and if these in turn influence child outcomes. Aim 3. To assess whether baseline parent characteristics (financial stress, mental health, relationship conflict), child characteristics, or program processes (fidelity, parent engagement) moderate outcomes.